This case relates generally to document feeders for picking sheets of documents already having data thereon, and more particularly to scanning units in a facsimile machine.
Prior art scanning units have typically had a myriad of parts making up the document path. This has typically resulted in complicated referencing between adjoining parts which produces larger tolerance variations. Accordingly, misfeeds often occur, and the quality of scanning is often unsatisfactory, thereby resulting in bad outputs such as at a facsimile receiver.
Prior solutions have failed to adequately deal with the problem, and the multiple parts have required more intervention during assembly of the products, and greater paper path disruption, as well as imprecise referencing between elements on a rigid frame and matching elements on an upper document guide which is typically move between a closed scanning position and an open position to allow manual accessibility.
What is needed is a document picking and transport system which provides the advantages of improved reliability and output quality due to decreased assembly time and intervention, decreased part count, decreased interruption of the document path, and improved document control while scanning.
In a scanning unit such as a facsimile machine, an automatic document feeder transports individual sheets from a stack of documents along a document path over a scanning window to an output tray. An upper guide member includes an integrated chassis which provides most of the functional features required for picking individual sheets from a stack of documents in an input tray and transporting the sheet past a scanning window. The various components incorporated in the integrated chassis include a document separation mechanism, pre-scanning pinch rollers, post-scanning pinch rollers, a spring-loaded limiter with minimal paper path obstruction, a hinging mechanism to facilitate manual access to the document path, a latching mechanism, referencing datums, and ESD grounding including ESD elements adjacent the document path and an ESD shield for a circuit board housed in the upper guide member. In the preferred form, the integrated chassis is formed from an enlarged sheet metal plate which attaches to the underside of a manual control/display panel with the circuit board sandwiched therebetween, which moves from a closed position during feeding, transporting and scanning to an open position for removing any paper jams in the document path, and for maintenance on the scanner such as cleaning the scanning window and the whitened surface on the limiter.